From the prior art, hybrid vehicles comprising a hybrid drive are known. Besides the internal combustion engine they comprise at least one electric motor or electric machine. In serial hybrid vehicles a generator supplies electrical energy to the electric motor that drives the wheels. In addition parallel hybrid vehicles are known, in which the torques of the internal combustion engine and of at least one electric machine that can be connected to the internal combustion engine are added. In this case the electric machines can be connected to the belt drive or to the crankshaft of the internal combustion engine. The torques produced by the internal combustion engine and/or the at least one electric machine are transmitted to the driven axle by a downstream transmission.
For example, from DE 102006019679 A1 a drivetrain with an electrically controllable hybrid drive and an electro-hydraulic control system, a number of electric power units and a number of torque transmission mechanisms is known. In this case the torque transmission mechanisms can be selectively engaged by the electro-hydraulic control system to produce four forward gears, a neutral condition, an electric operating mode with low and high rotation speeds, an electrically adjustable operating mode with low and high rotation speeds, and an uphill operating mode.
From DE 102005057607 B3 a hybrid drive for vehicles is known, which comprises at least a main motor, in particular an internal combustion engine, a generator, an electric motor and a planetary transmission comprising a sun gear, a ring gear, a planetary gear carrier and planetary gearwheels, which has at least one drive output shaft. In this case it is provided that for a first driving range of the vehicle, in order to add the torques, the driveshafts of the main motor and of the electric motor are coupled to the sun gear of the planetary transmission, and for a further driving range one of the two motors can be coupled by frictional means to the ring gear of the planetary transmission for the mechanical addition of the rotation speeds in accordance with the superimposition principle.
In vehicles comprising an automated transmission, the transmission input must be free from load before a gear can be disengaged; furthermore, before the new gear can be engaged the transmission input must be synchronized.
According to the prior art a shift with traction force interruption is carried out in hybrid vehicles with an automated transmission during hybrid operation by eliminating the load at the internal combustion engine and the electric machine in a first step, and then decoupling the internal combustion engine from the drivetrain by disengaging a clutch. When the internal combustion engine has been decoupled the old gear is disengaged and the speed of the electric machine is adjusted to the synchronous speed, the new gear is then engaged, the internal combustion engine is re-coupled, and finally the load at the internal combustion engine and the electric machine is built up again.